This invention relates to curable fluoropolyether rubber compositions which cure into parts having good water repellency, oil repellency, heat resistance, solvent resistance, chemical resistance, weather resistance and parting property as well as improved acid resistance.
Japanese Patent No. 2,990,646 (JP-A 8-199070) discloses a composition comprising (A) a straight-chain fluoropolyether compound having at least two alkenyl groups in a molecule and a perfluoroalkyl ether structure in the backbone, (B) an organosilicon compound having at least two Hxe2x80x94SiOSi structures in a molecule, and (C) a hydrosilylation catalyst, which cures into parts having a good profile of heat resistance, chemical resistance, solvent resistance, parting property, water repellency, oil repellency and weather resistance.
Although this fluoropolyether rubber composition performs well in most applications, a need for higher acid resistance exists in special applications associated with semiconductors, engine oils and the like where acid resistance is necessary.
An object of the invention is to provide curable fluoropolyether rubber compositions which cure into parts having good heat resistance, chemical resistance, solvent resistance, parting property, water repellency, oil repellency and weather resistance as well as improved acid resistance.
It has been found that by compounding (A) a straight-chain fluoropolyether compound having at least two alkenyl groups in a molecule and a perfluoropolyether structure in the backbone, (B) an organosilicon compound having in a molecule at least two silicon atom-bonded hydrogen atoms, which all form Hxe2x80x94SiCH2xe2x80x94 structures, and (C) a hydrosilylation catalyst, there is obtained a curable fluoropolyether rubber composition which cures into parts having good heat resistance, chemical resistance, solvent resistance, parting property, water repellency, oil repellency and weather resistance as well as improved acid resistance.
Fluoropolyether rubber compositions using an organosilicon compound having Hxe2x80x94SiOSi structures as disclosed in Japanese Patent No. 2,990,646 are not so strong against acid since the SiOSi linkage can undergo silicon-oxygen cleavage under the action of acid. By contrast, in the organosilicon compound having Hxe2x80x94SiCH2xe2x80x94 structures, the silicon-carbon bond is highly stable against acid. Thus use of the organosilicon compound having Hxe2x80x94SiCH2xe2x80x94 structures provides a fluoropolyether rubber composition with excellent acid resistance.
Accordingly the invention provides a curable fluoropolyether rubber composition comprising
(A) a straight-chain fluoropolyether compound having at least two alkenyl groups in a molecule and a perfluoropolyether structure in the backbone,
(B) an organosilicon compound having in a molecule at least two silicon atom-bonded hydrogen atoms, which all form Hxe2x80x94Si(CH2)cxe2x80x94 structures, wherein c=1 to 4, and
(C) a hydrosilylation catalyst.
Component (A) of the curable fluoropolyether rubber composition according to the invention is a straight-chain fluoropolyether compound having at least two alkenyl groups in a molecule and a divalent perfluoroalkyl ether structure in the backbone.
The perfluoroalkyl ether structure may be a structure comprising a multiplicity of recurring units: xe2x80x94CdF2dOxe2x80x94 wherein d in each unit is independently an integer of 1 to 6, for example, a structure of the following general formula (5):
(CdF2dO)qxe2x80x83xe2x80x83(5)
wherein q is an integer of 1 to 500, preferably 2 to 400, and more preferably 10 to 200.
The recurring units xe2x80x94CdF2dOxe2x80x94 constituting the structure of formula (5) are exemplified by the following units:
xe2x80x94CF2Oxe2x80x94,
xe2x80x94CF2CF2Oxe2x80x94,
xe2x80x94CF2CF2CF2Oxe2x80x94,
xe2x80x94CF(CF3)CF2Oxe2x80x94,
xe2x80x94CF2CF2CF2CF2Oxe2x80x94,
xe2x80x94CF2CF2CF2CF2CF2CF2Oxe2x80x94, and
xe2x80x94C(CF3)2Oxe2x80x94,
Of these, xe2x80x94CF2Oxe2x80x94, xe2x80x94CF2CF2Oxe2x80x94, xe2x80x94CF2CF2CF2Oxe2x80x94 and xe2x80x94CF(CF3)CF2Oxe2x80x94 are especially preferred. It is noted that the perfluoroalkyl ether structure may be comprised of such recurring units of one type or a combination of two or more types.
The alkenyl groups in the straight-chain fluoropolyether compound (A) are preferably those groups having 2 to 8 carbon atoms, especially 2 to 6 carbon atoms, and terminated with a CH2xe2x95x90CHxe2x80x94 structure, for example, vinyl, allyl, propenyl, isopropenyl, butenyl, and hexenyl. Of these, vinyl and allyl are preferred. The alkenyl groups may be located at any position within the molecule, but preferably attached to opposite ends of the molecular chain. In this preferred arrangement, the alkenyl groups may be attached to opposite ends of the straight-chain fluoropolyether compound backbone directly or through a divalent linking group: xe2x80x94CH2xe2x80x94, xe2x80x94CH2Oxe2x80x94 or xe2x80x94Yxe2x80x94NRxe2x80x94COxe2x80x94. Herein Y is xe2x80x94CH2xe2x80x94 or a group of the following structural formula (Z): 
(wherein the free valence bond may be at the o, m or p-position), and R is hydrogen, methyl, phenyl or allyl.
The fluoropolyether compound (A) is preferably a straight-chain one of the following general formula (2) or (3).
CH2xe2x95x90CHxe2x80x94(X)pxe2x80x94Rf0xe2x80x94(X)pxe2x80x94CHxe2x95x90CH2xe2x80x83xe2x80x83(2)
CH2xe2x95x90CHxe2x80x94(X)pxe2x80x94Qxe2x80x94Rf0xe2x80x94Qxe2x80x94(X)pxe2x80x94CHxe2x95x90CH2xe2x80x83xe2x80x83(3)
Herein X is independently xe2x80x94CH2xe2x80x94, xe2x80x94CH2Oxe2x80x94 or xe2x80x94Yxe2x80x94NRxe2x80x2xe2x80x94COxe2x80x94 wherein Y is xe2x80x94CH2xe2x80x94 or a group of the following structural formula (Z): 
(o, m or p-position), and Rxe2x80x2 is hydrogen, methyl, phenyl or allyl. Rf0 is a divalent perfluoropolyether structure, preferably of the formula (5), that is, (CdF2dO)q. Letter p is independently 0 or 1. Q is a divalent hydrocarbon group of 1 to 15 carbon atoms which may contain an ether bond, for example, an alkylene group or an alkylene group containing an ether bond.
Of these straight-chain fluoropolyether compounds (A), those of the following general formula (4) are preferred. 
Herein X is independently xe2x80x94CH2xe2x80x94, xe2x80x94CH2Oxe2x80x94 or xe2x80x94Yxe2x80x94NRxe2x80x2xe2x80x94COxe2x80x94 wherein Y is xe2x80x94CH2xe2x80x94 or a group of the following structural formula (Z): 
(o, m or p-position), and Rxe2x80x2 is hydrogen, methyl, phenyl or allyl. Letter p is independently 0 or 1, r is an integer of 1 to 6, u is an integer of 2 to 6, and m and n each are an integer of 0 to 200.
Desirably the straight-chain fluoropolyether compounds of formula (4) have a weight average molecular weight of about 4,000 to 100,000, more desirably about 1,000 to 50,000.
Illustrative, non-limiting, examples of the straight-chain fluoropolyether compounds of formula (4) are given below. In the formulas, m and n are as defined above. 
In the practice of the invention, to tailor the straight-chain fluoropolyether compound of formula (4) to a weight average molecular weight desired for a particular purpose, it is possible that the straight-chain fluoropolyether compound be previously subjected to hydrosilylation reaction with an organosilicon compound having two SiH groups in a molecule by a conventional method under ordinary conditions to form a chain-extended product, which can be used as component (A).
Component (B) serves as a crosslinking agent and chain extender for component (A). Any desired organosilicon compound may be used as long as it has at least two silicon atom-bonded hydrogen atoms in a molecule in which every silicon atom-bonded hydrogen atom forms an Hxe2x80x94Si(CH2)c, wherein c=1 to 4, structure. The organosilicon compound is preferably of the following general formula (1). 
Herein c is 1, 2, 3 or 4. R is a monovalent hydrocarbon group of 1 to 20 carbon atoms, preferably 1 to 6 carbon atoms, and may be the same or different. Z is hydrogen or xe2x80x94Qxe2x80x94M, xe2x80x94Qxe2x80x94Rf, xe2x80x94Qxe2x80x94, xe2x80x94Rfxe2x80x2xe2x80x94 or xe2x80x94Qxe2x80x94Rfxe2x80x2xe2x80x94Qxe2x80x94 wherein Q is a divalent hydrocarbon group of 1 to 15 carbon atoms which may contain an ether bond, Rf is a monovalent perfluoroalkyl or perfluorooxyalkyl group, and Rfxe2x80x2 is a divalent perfluoroalkylene or perfluorooxyalkylene group. Letter s is 1, 2 or 3, t is 0, 1, 2 or 3, and a and b each are 0 or 1, with the proviso that a and b are not 0 at the same time.
The hydrocarbon groups represented by R will be described later in detail. Examples of Q include alkylene groups such as methylene, ethylene, propylene and hexylene, and those alkylene groups whose chain is separated by an ether bond (xe2x80x94Oxe2x80x94). The monovalent perfluoroalkyl and perfluorooxyalkyl groups represented by Rf and the divalent perfluoroalkylene and perfluorooxyalkylene groups represented by Rfxe2x80x2 will also be described later in detail.
Illustrative examples of the organosilicon compound are given below. In the formulas, Me is methyl. 
In consideration of compatibility with and dispersibility in component (A) and uniformity after curing, there may be used those organosilicon compounds having at least one monovalent perfluoroalkyl, monovalent perfluorooxyalkyl, divalent perfluoroalkylene or divalent perfluorooxyalkylene group in a molecule.
The perfluoroalkyl, perfluorooxyalkyl, perfluoroalkylene and perfluorooxyalkylene groups are exemplified by those of the following general formulas. Monovalent perfluoroalkyl
CgF2g+1xe2x80x94
g is an integer of 1 to 20, preferably 2 to 10. Divalent perfluoroalkylene
xe2x80x94CgF2gxe2x80x94
g is an integer of 1 to 20, preferably 2 to 10. Monovalent perfluorooxyalkyl 
n is an integer of 1 to 5. Divalent perfluorooxyalkylene 
The sum of m+n is an integer of 1 to 200.
xe2x80x94(CF2O)mxe2x80x94(CF2CF2O)nxe2x80x94CF2xe2x80x94
Each of m and n is an integer of 1 to 50.
These perfluoro(oxy)alkyl and perfluoro(oxy)alkylene groups may be attached to silicon atoms either directly or through divalent linking groups. Such divalent linking groups are alkylene and arylene groups and combinations thereof, which may have an intervening bond such as an ether bond-forming oxygen atom, amide bond, carbonyl bond or the like. Illustratively, divalent linking groups having 2 to 12 carbon atoms are preferred, examples of which are given below.
xe2x80x94CH2CH2xe2x80x94
xe2x80x94CH2CH2CH2xe2x80x94
xe2x80x94CH2CH2CH2OCH2xe2x80x94
xe2x80x94CH2CH2CH2xe2x80x94NHxe2x80x94Cxe2x80x94
xe2x80x94CH2CH2CH2xe2x80x94N(Ph)xe2x80x94Cxe2x80x94
xe2x80x94CH2CH2CH2xe2x80x94N(CH3)xe2x80x94Cxe2x80x94
xe2x80x94CH2CH2CH2xe2x80x94Oxe2x80x94Cxe2x80x94
Note that Ph is phenyl.
In addition to the monovalent organic group containing a mono- or divalent fluorinated substituent, that is, perfluoroalkyl, perfluorooxyalkyl, perfluoroalkylene or perfluorooxyalkylene group, the organosilicon compound (B) has the silicon atom-bonded monovalent substituent R, which is selected from substituted or unsubstituted hydrocarbon groups of 1 to 20 carbon atoms. Exemplary hydrocarbon groups are alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, cyclohexyl, octyl and decyl, alkenyl groups such as vinyl and allyl, aryl groups such as phenyl, tolyl and naphthyl, aralkyl groups such as benzyl and phenylethyl, and substituted ones of the foregoing groups in which some hydrogen atoms are substituted with chlorine atoms, cyano groups or the like, such as chloromethyl, chloropropyl and cyanoethyl.
With respect to the organosilicon compound, the number of silicon atoms per molecule is usually about 2 to about 60, preferably about 3 to about 30, though not limited thereto.
The following examples are also typical of the organosilicon compounds. They may be used alone or in admixture of two or more. Note that Me is methyl and Ph is phenyl. 
An appropriate amount of component (B) blended is such that 0.5 to 5 mol, especially 1 to 2 mol of hydrosilyl groups (or SiH groups) in component (B) are available per mol of alkenyl groups (e.g., vinyl, allyl and cycloalkenyl) in component (A). Less amounts of component (B) may achieve an insufficient degree of crosslinking whereas excessive amounts of component (B) may allow chain lengthening to become preferential, inviting short curing and foaming, and aggravating heat resistance, compression set and the like.
Component (C) is a hydrosilylation catalyst, which is typically selected from transition metals, for example, platinum group metals such as Pt, Rh and Pd and compounds of these transition metals. Because these compounds are generally expensive noble metal compounds, the invention favors the use of platinum compounds which are readily available.
Exemplary platinum catalysts are chloroplatinic acid, complexes of chloroplatinic acid with olefins such as ethylene, and complexes of chloroplatinic acid with alcohols and vinylsiloxane, as well as platinum on silica, alumina and carbon, though not limited thereto.
Platinum group metal compounds other than the platinum compounds include rhodium, ruthenium, iridium and palladium compounds, for example, RhCl(PPh3)3, RhCl(CO)(PPh3)2, RhCl(C2H4)2, Ru3(CO)12, IrCl(CO)(PPh3)2, and Pd(PPh3)4 wherein Ph is phenyl.
The amount of the catalyst used is not critical and a catalytic amount may achieve a desired curing rate. From the economical standpoint and to obtain satisfactory cured parts, the catalyst amount is preferably about 0.1 to 1,000 ppm, more preferably about 0.1 to 500 ppm of platinum group metal based on the entire curable composition.
In addition to component (B), the curable composition of the invention may have another crosslinking agent and chain extender for component (A). Specifically, an organosilicon compound having in a molecule at least two SiH structures not corresponding to component (B), typically Hxe2x80x94Sixe2x80x94OSi structures, may be blended for ease of working and tailoring rubber physical properties. Such a SiH-bearing organosilicon compound not corresponding to component (B) is not critical as long as it has at least two SiH groups in a molecule. It may have a chain, cyclic or network structure.
Where an organosilicon compound having hydrosilyl groups or SiH groups is added as a crosslinking agent and chain extender for component (A) in addition to component (B), the amount of this additional organosilicon compound is preferably such that the total amount of SiH groups (available from component (B) and additional organosilicon compound) is 0.5 to 5 mol, especially 1 to 2 mol per mol of alkenyl groups (e.g., vinyl, allyl and cycloalkenyl) in component (A). Less amounts of SiH groups may achieve an insufficient degree of crosslinking whereas excessive amounts of SiH groups may allow chain lengthening to become preferential, inviting short curing and foaming, and aggravating heat resistance, compression set and the like.
The proportion of component (B) to the additional organosilicon compound having SiH structures is not critical and may be set as appropriate depending on a particular application.
If desired, various additives may be added to the inventive curable composition for improving its practical usage. For instance, polysiloxanes containing CH2xe2x95x90CH(R)SiO units wherein R is hydrogen or a substituted or unsubstituted monovalent hydrocarbon group (see JP-B 48-10947) and acetylene compounds (see U.S. Pat. No. 3,445,420 and JP-B 4-3774) are added for the purpose of controlling the curing rate of the curable compositions. Other useful additives are ionic compounds of heavy metals (see U.S. Pat. No. 3,532,649).
To the curable composition of the invention, fillers may be added for the purposes of reducing thermal shrinkage upon curing, reducing the coefficient of thermal expansion of the cured elastomer, improving thermal stability, weather resistance, chemical resistance, flame retardance or mechanical strength, and/or lowering the gas permeability. Exemplary additives include fumed silica, quartz flour, glass fibers, carbon, metal oxides such as iron oxide, titanium oxide and cerium oxide, and metal carbonates such as calcium carbonate and magnesium carbonate. If desired, suitable pigments and dyes are added.
The method of preparing the curable composition according to the invention is not critical. The composition may be prepared simply by mixing the above-described components. The composition may be formulated as two parts, one part consisting of component (A) and components (B) and (C) and the other part consisting of components (A) and (C), which are to be combined together on use. For the composition to cure, room temperature cure is possible depending on the type of functional group in component (A) and the type of catalyst (C) although a common, preferred practice is to heat the composition at about 100 to 200xc2x0 C. for several minutes to several hours for curing.
On use, depending on its particular application and purpose, the curable composition may be dissolved in a suitable fluorochemical solvent, for example, 1,3-bistrifluoromethylbenzene or perfluorooctane in a desired concentration before it is applied.
The curable fluoropolyether rubber composition cures into parts which have good heat resistance, chemical resistance, solvent resistance, parting property, water repellency, oil repellency and weather resistance as well as improved acid and alkali resistance. The composition is mi thus useful in a variety of molding applications, for example, as sealants for semiconductor manufacturing apparatus, O-rings, diaphragms and sealants for automobiles and aircraft, roll materials for copiers, and constituent materials for secondary cells and fuel cells.